The influence of taurine and L-carnitine on 6 β-hydroxycortisol/cortisol ratio in human urine of healthy volunteers.

Background Cytochrome P450s (CYPs, EC 1.14.14.1) are the main enzymes of drug metabolism. The functional significance of CYPs also includes the metabolism of foreign chemicals and endogenic biologically active compounds. The CYP3A4 isoform contributes to the metabolism of about half of all marketed medicinal preparations. The aim of this study was to investigate the effects of two biologically active compounds: 2-aminoethane-sulfonic acid (taurine) and 3-hydroxy-4-trimethylaminobutyrate (L-carnitine) on urinary 6β-hydroxycortisol/cortisol (6β-OHC/cortisol) metabolic ratio as a biomarker of the CYP3A4 activity of healthy volunteers. Taurine is used for the treatment of chronic heart failure and liver disease. Cardiologists, nephrologists, neurologists, gerontologists in addition to the main etiopathogenetic therapies, use L-carnitine. The quantification of the 6β-OHC/cortisol metabolic ratio as a biomarker of CYP3A4 activity in human urine was used for the assessment of CYP3A4 catalytic activity as a non-invasive test. Methods The study included 18 healthy male volunteers (aged from 18 to 35 years old). The volunteers took taurine in a dose of 500 mg twice a day or L-carnitine in a dose of 2.5 mL 3 times a day for 14 consecutive days. The test drug was given 20 min before meals. The collection of urine samples was performed before and after 3, 7, 10, and 14 days after taurine intake. The metabolic ratio of 6β-OHC/cortisol in morning spot urine samples was studied by the liquid chromatography/mass spectroscopy (LC/MS) method. Results The ratio of 6-6β-OHC/cortisol was used as a biomarker to study the taurine and L-carnitine influence on CYP3A4 metabolism of cortisol. The ratio of urinary 6β-OCH/cortisol in the morning urine samples of volunteers before the beginning of taurine therapy (baseline ratio) was 2.71 ± 0.2. Seven days after the administration of taurine in a dose of 500 mg twice a day, the 6β-OCH/cortisol ratio was 3.3 ± 0.2, which indicated the increased catalytic activity of CYP3A4 towards cortisol. As for the L-carnitine supplementation, analysis of the 6β-OCH/cortisol ratio in the urine for 14 days did not show any significant changes in this baseline ratio, indicating the lack of L-carnitine influence on the catalytic activity of CYP3A4 to cortisol. Conclusions The results obtained demonstrated the influence of taurine on 6β-OCH/cortisol metabolic ratio as a biomarker of CYP3A4 catalytic activity to cortisol. L-carnitine did not affect the activity of CYP3A4. The lack of a clinically meaningful effect of L-carnitine was established.